1. Field of the Invention
The present invention relates to a monoblock cylinder head for a water-cooling type engine, and in particular to a monoblock cylinder head that does not form a clearance, through which non-combustion gas can enter, between the head and a piston in a joining inner circumferential surface of an upper end portion of a cylinder wall portion to a cylinder head ceiling portion.
2. Description of the Related Art
A monoblock cylinder head is frequently used for an aircraft engine.
To manufacture an engine main body, in general, as shown in FIG. 3, a cylinder block 40 and a cylinder head 41 are joined to each other by bolts with a cylinder gasket 42 interposed there between, thereby constructing an engine main body 43. In the drawing, reference numeral 44 denotes a head cover, and reference numeral 45 denotes an oil pan.
A monoblock cylinder head is formed from a cylinder block cylinder portion and a cylinder head by integrated molding using a casting die. The monoblock cylinder head can dispense with a plurality of bolt boss portions, bolts and a head gasket corresponding thereto, which are, otherwise required in a case where the cylinder block cylinder portion and the cylinder head are separated and thus joined to each other. Consequently, the monoblock can reduce the weight of the engine main body, and, for this reason, is frequently used, in particular, for an aircraft engine.
As shown in FIG. 4, in the monoblock cylinder head 46 of this type, a stress concentration acts on a joining portion 52 between a cylinder head ceiling portion 49 and a cylinder wall portion 48, which is caused due to combustion pressure applied to the cylinder head ceiling portion 49 and the upper portion of the cylinder wall portion 48. To relax this stress concentration, an annular groove portion 57 having a predetermined radius of curvature is formed circumferentially in an inner circumferential surface of the joining portion 52 of the monoblock cylinder head 46.
In a case where the joining portion 52 is formed to have the predetermined radius of curvature, even if a piston 53 reaches an upper dead point in the upper end portion of a cylinder 55 as shown in FIG. 5, an annular space portion 56 is formed along the inner circumferential surface of the cylinder 55 between a piston circumferential surface portion 54 and the inner circumferential surface portion of the annular groove portion 57. Consequently, non-combustion gas enters into this annular space portion 56, so that it causes disadvantages decreasing the combustion efficiency, the fuel consumption efficiency and the exhaust emission.
Accordingly, an object of the present invention is to provide a monoblock cylinder head, which can relax stress concentration caused by generated combustion load on a joining portion between a cylinder head ceiling portion and a cylinder upper end portion, and which can develop the combustion efficiency to improve the fuel consumption efficiency as well as improve the exhaust emission.
To attain the object as noted above, according to the present invention, there is provided amonoblock cylinder head for an engine, in which a cylinder upper end portion and a cylinder head ceiling portion are formed integrally, the monoblock cylinder head comprising an annular groove portion, having such a radius of curvature as to be capable of supporting load generated by combustion in a combustion chamber within a cylinder, that is circumferentially provided in an inner circumferential surface of a joining portion of an upper end portion of a cylinder wall portion to the cylinder head ceiling portion, and an engagement member, having an inner circumferential surface portion capable of forming substantially the same plane as a cylinder interior surface, that is engaged with the annular groove portion.
Accordingly, in the present invention, since the engagement member is engaged with the annular groove portion, and the inner circumferential surface portion of this engagement member forms substantially the same plane as the cylinder interior surface, the upper end portion of the cylinder wall portion and the cylinder head ceiling portion are jointed to each other continuously and substantially perpendicularly.
For this reason, even if a piston is arrived at an upper dead point, there is formed no space portion in the joining portion of the upper end portion of the cylinder wall portion to the cylinder head ceiling portion, unlikely to the conventional monoblock cylinder head. Consequently, it is possible to prevent problems encountered in the prior art, in which the non-combustion gas enters into the space portion so that it causes to lower the combustion efficiency to lower the fuel consumption efficiency and to lower the exhaust emission.
The construction of the monoblock cylinder head according to the present invention is effectively applied, in particular, to a so-called liner-less type monoblock cylinder head different from a type in which, after a monoblock cylinder head is formed by integrated molding, a separate cylinder liner is inserted into a cylinder.
That is, in a case where a monoblock cylinder head is cast to have an annular groove portion having a predetermined radius of curvature in an inner circumferential surface portion of a joining portion of a cylinder side wall to a cylinder head ceiling portion, and then a separate cylinder liner is insertion disposed within the cylinder so that the cylinder has the liner, the annular groove portion is covered by the cylinder liner during a honing process, and accordingly similarly to the construction of the present invention, the cylinder head ceiling portion and the cylinder wall portion are joined to each other continuously and substantially perpendicularly.
However, the construction of the monoblock cylinder head according to the present invention is effectively applied to a so-called liner-less type monoblock cylinder head in which such a separate cylinder liner is not disposed within the cylinder.
Since the annular groove portion, having such a radius of curvature as to be capable of supporting load generated by combustion in the combustion chamber within the cylinder, is circumferentially provided in the inner circumferential surface of the joining portion of the upper end portion of the cylinder wall portion to the cylinder head ceiling portion, it is possible to relax the stress concentration caused on the joining portion of the upper end portion of the cylinder wall portion to the cylinder head ceiling portion when the combustion load is generated.
In the present invention, the engagement member is annular, and is fitted to substantially the entire circumference of the annular groove portion.
Accordingly, in the present invention, since the engagement member is fitted to the entire circumference of the annular groove portion, the presence of the space portion can be eliminated over the entire circumference.
In the present invention, the annular engagement member is formed to have a radius of curvature slightly larger than that of a cylinder inner circumferential surface portion, and is partly cut, so that the engagement member is engaged with the annular groove portion by an enlarging biasing force.
Accordingly, in the present invention, after the honing process is carried out for the cylinder head inner circumferential surface, the engagement member is deformed so that its inner diameter is reduced, and then inserted from the lower portion of the cylinder into the cylinder to be fitted into the annular groove portion, and thereafter engaged with the annular groove portion by enlarging the engagement member.
Consequently, the manufacture of the monoblock cylinder head that can improve the combustion efficiency to improve the fuel consumption efficiency and improve the exhaust emission, can be performed easily.
Further, in the present invention, the joining portion of the upper end portion of the cylinder wall portion to the cylinder head ceiling portion is bulged in a cylinder diametrical direction, and the annular groove portion is provided to an inner circumferential surface of the joining portion.
Accordingly, in the present invention, the annular groove portion is provided to the joining portion of the upper end portion of the cylinder wall portion to the cylinder head ceiling portion, and a predetermined wall thickness is secured for the joining portion. Consequently, the joining portion is constructed to sufficiently bear against the stress generated even in a case where the combustion load is applied.